This invention relates to a slow-acting rotary shaft device which supports a second member rotatably which rotates relatively with respect to a first member.
This slow-acting rotary shaft device is, for instance, used for a rotatably supporting portion of a hinge device of a compact case for makeup, a radio cassette, a dashboard of a car and the like.
Such type of a slow-acting rotary shaft device consists of a shaft 3 which supports a rotary member 1 rotatably which rotates relatively with respect to a fixed member 2 as shown in FIG. 6.
The shaft 3 approximately consists of, as shown in FIG. 7 and FIG. 8, a hollow shaft body 31, cap members 32 and 33 rotatably inserted outwardly to both sides of the shaft body 31, a torsion bar 4 latched to one end hook portion 41 in the shaft body 31, while latching another end hook portion 42 in the cap member 33, and a viscous grease (not shown) enclosed between the shaft body 31 and the cap members 32 and 33.
The shaft body 31 is provided with a shaft laving a stopped portion wherein small diameter shaft portions 31b where cap members 32 and 33 are inserted outwardly and rotatably therethrough are formed at both sides of a large diameter shaft portion 31a, and a slit penetrated hole 34 is formed in a longitudinal direction. The large diameter shaft portion 31a is provided with a projected key 35. The cap members 32 and 33 are formed to be cylinders having bottoms respectively, inner and outer diameters of said each cylinder being formed respectively to be an approximately same outer diameter of the small shaft portion 31b and the same outer diameter of the large diameter portion 31a. Each of the cap members 32 and 33 is respectively provided with a projected key portion 37 and 38 at the outer circumference thereof.
At the bottom of the cap member 33 is formed a slit concave 36. The cap members 32 and 33 are outwardly inserted to small diameter portions 31b and 31c, respectively, circular grooves 32a and 33a of cap members 32 and 33 being inserted over circular ribs 31c on each small diameter shaft portion 31b respectively to prevent it from falling off so that it may be rotatably incorporated to the shaft body 31.
In this incorporated state, the torsion bar 4 is inserted into the penetrated hole 34 of the shaft body 31, one hook portion 41 thereof being latched with Said penetrated hole 34, while another end hook portion 42 being latched with the concave 36 of the cap member 33, and the viscous grease is enclosed between cap members 32, 33 and small diameter shaft portions 31b, 31b respectively.
The shaft 3 thus incorporated is inserted into a pivotally supporting portion by standing up the rotary member 1 at 90.degree. with respect to the fixed member 2 so that key grooves (not shown) provided at each shaft supporting portion of the rotative member 1 and the fixed member 2 may correspond each other. By this insertion, the shaft 3 positions the large diameter shaft portion 31a of the shaft body 31 in the bearing portion 21 of the fixed member 2, places the cap members 32 and 33 in the rotatable supporting portions 11 and 12 of the rotative member respectively and then inserts each key 35,37 and 38 into key grooves (not shown) formed at bearing portion 21 and rotatably supporting portions 11 and 12 respectively whereby the large diameter shaft portion 31a and the cap members 32 and 33 are respectively attached to the bearing portion 21 and the rotatable supporting portions 11 and 12 inrotatably.
In the conventional slow-acting rotary shaft device thus constituted, a jumping up torque is storaged in the torsion bar 4 by the rotation of the rotative member 1 from the neutral point b to the closed direction, and the negative member 1 is fixed to the fixed member 2 with an appropriate locking means at the whole closed point a where the jumping up torque becomes max. (Please see FIG. 9). By this, the locking means is released, the rotative member 1 rotates in the opening direction by the jumping up torque of the torsion bar 4. At the time of this rotation, a shearing resistance of the viscous grease occurs and the rotative member 1 rotates with a slow-speed and can be stopped at the neutral point b in spite of the torque load of the torsion bar 4.
Thus, the conventional slow-acting rotary shaft can perform a slow-acting operation effectively at an area .alpha.1 from whole closing point a of the rotative member 1 to the neutral point b as shown in FIG. 9.
In such a hinge device, it is required to improve to a free stop area wherein the rotative member 1 can be stop at an any point in .alpha.2 area from the neutral point b to the whole opening point c by maintaining the max. rotation angle .alpha. of the rotative member 1 at approximately 135.degree. as shown in FIG. 9. In this case, it is impossible to satisfy this requirement by use of the conventional slow-acting rotary shaft device.
In other words, when the rotative member 1 is rotated from the neutral point b to the whole opening point c, the torsion bar 4 in the shaft 3 is twisted in the neutral direction against the closing direction at the time of the rotation in the .alpha.1 area described above whereby the torque is storaged in the torsion bar 4. The storaged torque operates to return the rotary member 1 in the neutral point b direction against the shearing resistance of the viscous grease. Accordingly, it is impossible to stop tile rotative member 1 at any point.
Further, when the rotative member 1 is rotated in the whole areas of the area .alpha.1 and the area .alpha.2 by aid of the torque of the torsion bar 4 by providing an initial torque to the torsion bar 4, the rotation moment of the rotative member 1 coincides with an operation direction of the torque of the torsion bar 4 in the .alpha.2 area whereby it is impossible to stop the rotative member 1 at any point by only the shearing resistance of the viscous grease.
Furthermore, the torsion bar 4 is restrained a twisting direction at the time of use by setting. This occurs such problem as a fact that when a rotation angle in .alpha.2 area increases the endurance of the torsion bar 4 decreases by the occurrence of the permanent setting.
This invention is performed in view of such case. The object of this invention is to provide a slow-acting rotary shaft device which is used for a pivotally supporting portion of a hinge device wherein the rotation angle of the rotative member exceeds the neutral point and enables to be a free stop area which is possible to rotate the rotative member with a slow-acting speed by the jumping up torque of the torsion bar in the rotary area within the neutral point and is possible to stop the rotative member at any point in the rotation area exceeds the neutral point thereof.